METABOLISM OF 25-HYDROXYVITAMIN D3 DURING PHOTOINDUCED REPRODUCTIVE DEVELOPMENT IN FEMALE JAPANESE QUAIL

Synchronous development of the reproductive tract in adult female Japanese quail has been achieved by manipulation of photoperiod length. This has made possible determination of changes in vitamin D metabolism associated directly with the onset of reproductive maturity. The distribution of polar metabolites of 25-hydroxy [3H] vitamin D3 ([3H]-25-OH-D3) was altered shortly before the onset of egg laying, such that the specific activity of the 25-OH-D3-1α-hydroxylase increased 390%, while the production of 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] and an unidentified metabolite (metabolite IV) decreased 37 and 61% respectively. In addition, kidneys of reproductively mature female quail produced a metabolite, tentatively identified as 1,24,25-trihydroxyvitamin D3 [1,24,25(OH)3D3], which was not found in the kidneys of male quail or in those of female quail with immature oviducts. The concentration of oviduct nuclear estrogen receptor-estrogen complex increased to a level comparable to laying female quail very early in reproductive tract development. A 280% increase in kidney size occurred concurrently. In contrast, the altered renal metabolism of [3H]-25-OH-D3 did not occur until much later in development, suggesting that kidney growth and renal metabolism of vitamin D are independently regulated. It appears that the increased specific activity of the 25-OH-D3-1α-hydroxylase immediately prior to egg laying is important in the provision of calcium for shell formation. The close temporal relationship between the altered metabolism of [3H]25-OH-D3 and the onset of medullary bone formation suggests that a vitamin D metabolite may mediate the formation and utilization of medullary bone. © 1979.